5-bolt cranksets - lil' help?

My (ancienne) bike currently has a 52-42 at the front and 26/13, 7 speed at the back. I'm thinking of entering the Jennings Rivers Ride next month, and it's been pointed out that with my bottom gear being 52", I may not have enough leverage to get over Honister.

I've been thinking about solutions (on a tight budget), and one that seems to stand out is buying a chainring in the region of 36 or 38T and fitting it in place of the current 42T. However, I'm not sure it's that simple, so help me out. The cranks are 5 bolt, but do all 5-bolt cranks have the bolts in the same place (the circle of bolts has the same diameter), such that all 5-bolt rings are interchangeable, or do different companies have different standards?

TL;DR Are all 5-bolt chainrings interchangeable?

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TheHatter[770 posts]6 years ago

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I don't think you'll be able to get a 36 as they have a different placement for the bolts - the term is BCD (bolt circle diameter) and it may be stamped somewhere on the chanset. Your chainset is likely a standard rather with a BCD of 130 and to fit a 34 or 36 you'd need a BCD of 110. You should be able to fit a 38 though.

There are exceptions to the above and I have seen some older chainsets with very small BCD's which would allow you to fit a small chainring.

I find replacement chainrings are very expensive for what they are and you may be better off spending a bit more for a cheap compact chainset that will give you a much better range of gears- 34/50 is a typical setup. You can pick up some square taper ones on ebay for not much which would mean minimal changes to your bike.

Okay, I'd been seeing BCD numbers while browsing eBay but never figured out what it meant, silly boy. I can't find it printed on the chainset but a quick measure up indicates it's a 130mm, which puts the 36T possibility out. I may have a poke around eBay and my LBS to see if I can find a 38T that will fit. A 38T would give me 38" as my bottom gear, which is okay.

I thought about the idea of a new chainset but finding one in the right sizes, square taper, cheap etc. will be a bugger. Thanks Hatter, you've been very helpful

I run campy and being OLD I have 39T inner and 46T outer... on a 13/26 cassette

If a med cage on the rear derailleur then the world is your oyster... you could change the rear cassette to MANY combinations... but I would also replace the chain at the same time... (its a bit like changing the OIL in the motor every twelve months)

confused ..... well the only way i've dealt with gear ratios is buying lots of cassettes/chain rings and trying it out... (it's a ALOT like saddle selection)

Shimano, I think. It's not marked on the chainset but it's a Shimano gruppo. I can get a 39T 130mm BCD ring on CRC for £11. I'm going to nip to the LBS in the morning and see what I can find there. I'm also considering nicking one of the 28/14 cassettes off my mountain bikes and putting that on, it'll lose me some top speed but for this event that probably won't be a consideration And yeah, a new chain wouldn't hurt while I'm at it... I love my 52T big ring though. Sur la plaque!